Plastic molding machine



Feb. 16, 1954 R. w. MILER 2,668,986

PLASTIC MOLDING MACHINE Filed Aug. 22, 1952 N N N w go Q T 74 m l:

L N3 4 INVENTOR.

a BY R/c/mra W MI/er WJW ATTORNEYS Patented Feb. 16, 1954 PLASTIC MOLDING MACHINE Richard W. Miler, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application August 22, 1952, Serial No. 305,757

3 Claims. (01. 18-30) This invention relates to a machine for plasticating organic thermoplastic materials and forwarding them either to closed molds or to open extrusion orifices. It relates in particular to a machine which can be used, at will, as a plastics extruder, plastics injection molding press, or as a pump for viscous fluids such as molten plastics.

It is common practice, in the injection molding of plastics, to supply a charge of solid granules of the desired composition to the heated cylindrical barrel of an injection molding machine and then to push the plastic material rapidly, by means of a hydraulic ram, along the barrel and through a narrow annular space between a coaxial torpedo and the barrel, thence through a nozzle into a mold. The only opportunity for the material to become fluid is in the brief interval in which it is pushed, under high pressure, past the torpedo. As a consequence, it is generally recognized that there is need for improving the method of melting or plasticating the feed to an injection molding press if the output of the machine is to be of uniform quality. It was in an attempt to achieve the latter desired result that the machine of the present invention was developed.

The new machine, having a drive and feed end and a discharge end, comprises a heated and usually horizontal barrel extending through most of its length and having a feed opening near one end; a rotary screw, preferably compressive, in the barrel and extending forward from said feed end with only working clearance in the barrel; an elongated plasticating torpedo rotatable with the screw at the forward end of the screw; a ram coaxial with the screw and torpedo and adapted to slide longitudinally therein, said ram extending from outside the barrel at the feed end entirely through the screw and beyond the nose of the torpedo; radial and forwardly directed flow channels in the forward end of the ram, following the contour of the nose of the torpedo when the ram is retracted, converging at the axis of the ram and extending along said axis through its forward end; a cylindrical receiving chamber in the head of the machine coaxial with the main barrel thereof, extending from just beyond the tip of the torpedo to a plastics discharge port and being of a size to provide a sliding fit for the forward end of said ram; means for rotating the screw and torpedo; means for advancing the ram into said receiving chamber far enough to cut off communication between the barrel and chamber and to expel plastic from the chamber and for retracting the ram far enough to restore communication between the barrel and said chamher; and, optionally, means for decreasing the rate of rotation of the screw when the ram is advanced and for increasing it again when the ram is retracted.

The apparatus of the invention is illustrated in the annexed drawing, Fig, 1 of which is a longitudinal view of the entire machine in vertical section, while Fig. 2 is a similar but fragmentary view of a portion of the machine.

A feed opening Iii, through housing II into barrel I2 near the drive end I3 of the machine, delivers granular or other suitable plastic feed to a conventional forwarding screw I l. Barrel I2 is heated by any conventional means, not shown. An elongated torpedo I5, illustrated as being cylindrical, is attached as an extension to the forward end of screw I4 and is rotatable therewith. Torpedo I5 and the lands I6 of screw I4 have the usual small clearance in barrel I2, to shear the viscous film of plastic between the barrel and those rotating parts. Screw I 4 and its attached torpedo I5 are driven by conventional means, such as a variable speed drive, suitably through pinion ll, attached to rear bearing I8 just outside of housing II. Torpedo I5 and the hub of screw M are axially bored throughout their length, forming a second barrel or tunnel I9, coaxial with barrel I2. Barrel I2 tapers down at its forward end, following generally the contour of the tip of torpedo I5. The discharge end 20 of housing I I is bored at least as large as tunnel l9 and in alignment therewith, to provide a receiving chamber 2i between barrel I2 and the discharge port 22, illustrated as being in a conventional injection nozzle 23. A cylindrical ram 24, of a diameter to provide a snug sliding fit in tunnel I9, extends from a hydraulic cylinder 25 outside of pinion I1 through the entire length of tunnel I9, its forward tip 26 extending into receiving chamber 2|. When chamber 2i is larger than tunnel I9, the forward end 26 of ram 24 is made large enough to have a sliding fit in chamber 2|, as shown in Fig. 2. Forwardly directed flow channels 21 are drilled into ram 24 along lines following generally the contour of the tip of torpedo I5, said channels 21 converging at the axis of ram 24 in a single axial channel 28 in communication with receiving chamber 2i. If desired, channel 28 may be provided with a ball-check valve consisting of a seat 29, ball 30 and stop pin 3| to limit the travel of ball 30. A similar valve may be situated advantageously in nozzle 23. The forward and return strokes of ram 24 may be limited in the usual way by stops mounted on the portion of the ram between the hydraulic cylinder 25 and tunnel I9.

In operation as an injection molding machine,

the latter is full, the ram 24 is advanced, forc -i ing the plastic material through outlet port 22 and usually into a mold. Ram Musretracted to the illustrated position, and chamber; lt again begins to fill with plastic. Z-If, ,unfder. the"m Id ing conditions employed, it is necessary to ram 24 in its advanced position for any prolonged period, it is desirable toist'op; 'onzatvleast to diminish the rate of rotation of the feed screw l4 and torpedo l5 untiLram 24 can be retracted and communication is-restored between barrel 1 and; receiving chamber 2 l. fl hils' can :beac- "comp'lished through a variable I speed-drive acting through pinion ll. Since advanceu ofram '2 a distance equal to the {difllfitlbOf reliannels' 21 -effectively seals those channels against backfl'ow' f the -plastic-= material; the'- ;ball--check valve'30 may be omitted from the: leading .end of the ram, when-the receiving chamber isxof the same-diameter as tunnel l9 Ifdesir'ed, the apparatus can nausea a'sman Xtruder pr pump and this may conveniently be done in connection withmoldingoperations. Thus, the rammay remain retractedwhile hot plastic material fillsand "overflows chamber l. 2|, with port 2 2 in communication. with .'a1mo.ld:;of much greater- =capacity than chamber .2 l 'r-W hen such a mold has beenfilledxin that mannenit'he -'ram may be advanced to pack into the mold an additionalamount of the plastic -from:;chamr processes.

' The illustrated cylindrical torpedo Elfirmay be replaced by rotary torpedoes ,of'other'l'sha'pesi, including,=. but without limitation; the ,helically grooved mixing torpedoes-1 of 1 U. S.-.-Patents 2,453,088 and 2;607,0'7'7. ",iII1,-e8;ChtQaSB the forward; :end. of barrel. l2 Willmost advantageously follow approximately the contour 30f; the torpedo, .leavingzsuchv clearance as {is needed to permit .fiow of the hotplastic, :and providing-smooth zlands tov the: openings of channels .21. H

' The foregoing "description and the accompanying drawings. have been concerned with preferred lemb'odimentsfof the invention. 2 It is to be .understood that changes may be made as to shape, size and arrangement of parts, within the scope of the invention as defined in the appended claims.

5 I claim:

1. In a plasticating machine having a feed ,opening into, a workings-barrel near oneend, said barrelbeing constricted near; thQ-bthel' end of the machine, means for heating said barrel; a

forwarding screw for conveying plastics from the feed opening along the heated barrel; a rotary "-torpeddas: an extension on said screw Within ,l saifi ba lrel; and external means for driving said vtor 'efdo'; the improvement which cona longitu'dinal bore through the screw and torp do, a ram in said bore, coaxial with the's'crew andto'rp'edo and adapted to slide longitudinally therein, said ram extending from outsidethe barrel at the yfeed end entirely through the screw section and beyond the nose of the torpedo into 1 a-- receiving m m er; forwardly 'lirected radial flow channelsdn therajm beyb'nd but" following *thebbri-tdiir -;of= -th'e nose 015 --th'e 'to'r pefdo; converging at the axi's-of the-rain -=arid l 'ext'ending-falong said axis-through therw rd end; of the rar'n; abylindricaI receiving-chamber the head of f the machine; coaxial with the bore, 'through the screw and torpedo; extending from-the constricted endof the barrelto a lastics Zd' charge port; and means for advancing the ram into said receiving 'chamber fa'renoiigh -tbc'ut b rgcommumcauen between thebarreliaiid chamber and to expel p1 stic=-from the chamber and ro mmcung theram rare'nough to restore *c on'iinunication between-Whe barrel 1 and said chamber. p

v 2: The improved machin'e claimed claim 1, in; cooperation with meansf fo'r de'e reasing -the rate-of-rotation. of the screw when the -ramis 40 advanced and forincreasing it a ain: when the ram isretr'acted.

f 3". The "improved machine claimed: in? claim v1, wherein the -;receiving chamber=- is of" greater diameter than the bore through the: screw: :and

'45 torpedo, and wherein the forward eneromhe-ram Number g Name :"Date i 2,359,839 Goe'ssling 00173 '10;: a 119.44 FOREIGN PATENTS Number. Country Date a, 

